The current processes in the field of lithography requires shorter and shorter wavelengths because of the increasing trend to manufacture smaller and smaller structures for semiconductor devices such as DRAM chips. Usually, a resist, i.e. a chemical substance sensitive to light, is illuminated by a light source via a mask. A pattern on the mask (either a reflective mask or a transmission mask) is transferred to the light sensitive resist which in turn is used in further processing steps to generate the structures on a substrate.
For the illumination light with wavelengths of 248 nm, 193 nm or 157 nm are used. Those wavelengths are generally termed as deep UV light.
The latest step in the direction of smaller wavelengths is the usage of extreme ultra violet (EUV) light with wavelengths between 1to 50nm, in particular with a wavelength of 13.4nm. This EUV light is usually produced by the generation of plasmas. It is known e.g. to generate EUV light with the wavelength of 13.4nm with a Xenon gas ignited by a pulsed Nd:YAG Laser to produce a plasma.
The latest step in the direction of smaller wavelengths is the usage of extreme ultra violet (EUV) light with wavelengths between 1 to 50 nm, in particular with a wavelength of 13.4 nm. This EUV light is usually produced by the generation of plasmas. It is known e.g. to generate EUV light with the wavelength of 13.4 nm with a Xenon gas ignited by a pulsed Nd:YAG Laser to produce a plasma.
But it is also known that such EUV generating plasmas emit light at other wavelengths, in particular in the deep ultra violet range (100 to 300 nm). Resists used in lithography are generally not only sensitive for light of one particular wavelength but for light in a range of wavelengths. Therefore, a resist for EUV lithography exhibits also sensitivity for light at DUV wavelengths reducing the quality of the lithography result.